Isis and Merck are developing an antisense oligonucleotide for the potential treatment of hepatitis C virus (HCV) infection [305306]. As of March 2000, the lead from this program, ISI-14803, was being studied in a phase I/II trial where it was administered in three weekly 2-h infusions for 4 weeks [327913], [357823]. Based on these results Isis plans to evaluate the potential of ISIS-14803 in single-agent trials and in combination studies with PEGylated interferon and ribavirin, and in studies that will examine longer-term dosing with both i.v. and s.c. administration [412920]. In January 2000, Isis signed a binding letter of agreement with Elan to form a new subsidiary of Isis to develop ISIS-14803 [351881], [362727]. In October 2001, Isis reported that it had earned a $1.5 million research milestone payment from Merck for progress in this collaboration [426015].